Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these

2. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

3. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.376

0.6

0.4

4. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Stirling

Ericson

5. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Ammonia

Carbon dioxide

6. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

7. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

8. For obtaining high COP, the pressure range of compressor should be

Optimum

High

Any value

Low

9. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

10. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

Page 2 of 4

11. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

15 bar

8 bar

30 bar

12. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

13. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

14. Rating of a domestic refrigerator is of the order of

40 tons

0.1 ton

5 tons

10 tons

15. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

16. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Miniature sealed unit

Centrifugal

17. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

18. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

19. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Good electrical conductor

Large latent heat

Low boiling point

20. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

Evaporator tubes

Page 3 of 4

21. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

Above critical temperature

22. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

23. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

5°C

15°C

24. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

None of these

Positive

25. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

26. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Any one of the above

Equal to unity

27. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

28. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

29. In a lithium bromide absorption refrigeration system

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

30. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Super-cooling

Normal cooling

Page 4 of 4

31. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

9: 1

1: 3

32. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

33. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

34. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

35. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

36. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

37. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

38. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

39. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

40. The boiling point of ammonia is

-10.5°C

-77.7°C

-30°C

-33.3°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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